Acct-Delay-Time missing with RADIUS accounting

[Jouni Malinen]

On Mon, Feb 22, 2016 at 03:26:51PM +0000, Nick Lowe wrote:
> But that leaves you with a reliability issue where you get resends of
> an Accounting-On, Accounting-Off, Start, Stop... you don't know when
> the original event actually occurred.

What's the use case for being so careful about Accounting-On and
Accounting-Off? I understand wanting to get more accurate
Accounting-Start/Stop, but those already include the Event-Timestamp and
Acct-Session-Time attributes where the former gives you calendar time
from NAS and the latter gives you the real duration of the session in
seconds based on monotonic time on the NAS.

If there is a critical requirement of getting the correct calendar time
the session happened, I'd assume starting hostapd only after having
confirmed that NTP has synchronized the time would be acceptable (and if
necessary, stopping hostapd if time sync is somehow lost).

This is also talking about the case of having to retransmit accounting
messages which has a limit on how many times (and for how long) that is
done. As such, even in the worst case, the difference is limited to
couple of minutes and if someone needs to get more detailed information
on a specific session afterwards, it's likely to be able to get pretty
good estimate on the time based Event-Timestamp and RADIUS server
receive timestamp over number of frames from the same NAS..

In other words, I'm still missing a detailed description of a real world
use case that would justify the extra complexity on NAS on top of what's
already available in hostapd.

-- 
Jouni Malinen                                            PGP id EFC895FA